The Universe's first galaxies played a key role in shaping the environment in which we now find ourselves. They fostered the formation of the first stars, which died in spectacular explosions that enabled a new generation of smaller stars, orbited by rockier planets. And the galaxies themselves merged and grew, forming the large galaxies and clusters that populate the Universe today. But, despite their critical role in shaping the Universe, we've never actually been able to see one of them.

Slowly, that's changing. The Hubble Deep Field exposures have helped us spot galaxies from the Universe's early days. But now, a special Hubble project has used an intervening cluster of galaxies as a lens to spot what appears to be the most distant galaxy ever imaged, one that dates from just 425 million years after the Big Bang.

Since it takes light time to reach us from distant corners of the Universe, the further you look, the older the objects you see. The wavelength of the light also gets shifted towards the red by the expansion of the Universe, which stretches it out as it travels. As you get closer to the Big Bang, light that started out in the UV end of the spectrum gets pushed deeper and deeper into the infrared. To make these galaxies even harder to spot, the extreme distance means that very few photons actually make their way to Earth, so these objects are incredibly dim.

So, to spot the most distant galaxies, the Hubble team searched for objects that weren't visible in shorter wavelengths, but did appear at longer wavelengths. To handle the dimness problem, the authors pointed the Hubble at large galaxy clusters, which have enough mass to act as a gravitational lens. (The project is called CLASH, for Cluster Lensing and Supernova survey with Hubble.)

With the Hubble pointed at the galaxy cluster MACSJ0647.7+7015, they hit the jackpot: three distinct objects that only appeared in images taken with the telescope's two deepest infrared filters. After mapping the distribution of matter (dark and otherwise) in the foreground cluster, they were able to ascertain that all three were images of the same background object, which they termed MACS0647-JD. The foreground galaxy cluster magnified the object by factors of 8x, 7x, and 2x.

But was it an early galaxy, or simply an infrared-bright object? The team behind the discovery used the Spitzer telescope to confirm that the objects were dim throughout the infrared; the Hubble hadn't simply caught the tail end of the light from a bright infrared object. An unusual aspect of gravitational lenses also helped them rule out any transient events. In addition to providing different levels of magnification, the light paths for each of the three images take different amounts of time to reach the Earth. As a result, the difference in time between some of the images is about 50 years, long enough that a transient event would have changed in character.

With a distant galaxy being the most likely candidate, the researchers estimated its likely properties. Based on the red shift, the galaxy appeared to have been emitting light when the Universe was only 425 million years old. The galaxy is also tiny (relatively speaking), at only 600 light years across, and about 108 to 109 times the mass of the Sun. The Milky Way is 250 times larger in size, and at least 100 times more massive. This provides strong support to most models of galaxy evolution, which suggest that multiple rounds of mergers took place to build the massive galaxies we see around us today.

The authors can't say much more than that at this resolution, but they are already hoping that the James Webb telescope takes a closer look at it whenever it finally gets to orbit.